1. Field of the Invention
The present invention relates to a liquid crystal display capable of displaying an image by a light reflection mode and a light transmission mode.
2. Description of the Related Art
It was sufficient for the conventional display of portable equipment such as a portable telephone or a pager to be capable of displaying simple characters such as numerals and letters. However, in accordance with the drastic development in the IT technologies achieved in recent years, it is desirable for a small, light and thin display having a low power consumption and capable of displaying a high quality color image to be put to a practical use even in the field of portable equipment, particularly, a portable information terminal.
As a display meeting the requirement noted above, a reflection type liquid crystal display, for example, is considered hopeful and has already been put partly to a practical use. When used outdoors in the daytime, the reflection type liquid crystal display is capable of displaying an image that is visible easily. However, a light source is not included in the reflection type liquid crystal display, with the result that the image displayed in a dark place can be scarcely recognized. In other words, the reflection type liquid crystal display is limited by the environment of use.
As a countermeasure, proposed is a front light technology. In the front light technology, the display surface of the reflection type liquid crystal display is covered with a transparent planar light source so as to make up for the insufficient illuminance of the external light. In this technology, it is unnecessary to change the internal structure of the liquid crystal display. However, the quality of the image is lowered by the reduction in the amount of reflected light, the blurring of the image, the increase in the feeling of thickness (or depth), etc.
Jpn. Pat. Appln. KOKAI Publication No. 11-316382 discloses a liquid crystal display capable of displaying an image by utilizing both the light reflection and the light transmission modes. In the liquid crystal display, each of the pixel electrodes is formed by the combination of a light reflecting conductive film and a light transmitting conductive film. According to the liquid crystal display of the particular construction, an image is displayed by light reflection mode under an environment of high illuminance, and a backlight is lit under an environment of low illuminance to display an image by both light reflection mode and light transmission mode.
The liquid crystal display referred to above, which utilizes the light reflection mode and the light transmission mode in combination, permits displaying an image that can be recognized satisfactorily without depending on the illuminance of the external light. However, the light reflecting conductive film and the light transmitting conductive film, which are included in the particular liquid crystal display, are formed by independent processes so as to lower the yield and to increase the manufacturing cost of the liquid crystal display. In addition, it is necessary to superpose the light reflecting conductive film and the light transmitting conductive film one upon the other in the liquid crystal display of the particular construction, with the result that a marked reduction in reflectance is derived from the overlapping of these conductive films so as to make it difficult to obtain a bright image. Further, in the liquid crystal display utilizing the light reflection mode and the light transmission mode in combination, while certainly low in its power consumption compared with the liquid crystal display of the light transmission mode, the power consumption is not necessarily lowered sufficiently.